1. Field of the Invention
This invention relates to a flow control valve having an operating piston which is sealingly movably arranged in a bore and defines in the bore an inlet chamber connected to a pump and a control chamber connected to a work port of a slave unit, with the operating piston being prestressed by a governing spring in the direction towards the inlet chamber, said governing spring being arranged in the control chamber, and wherein the inlet chamber has a return aperture connected to a reservoir, which return aperture can be closed by the operating piston, and wherein the inlet chamber is connected with the control chamber by a by-pass line wherein a restrictor is provided.
2. Description of the Prior Art
Such flow control valves are generally known and are used in pressure fluid systems wherein the pump does not deliver a constant pressure fluid quantity although the dependant unit requires a certain pressure fluid flow within certain tolerances independant of the pressure. The different delivery quantity of the pump is for example caused by the fact that in a pressure fluid system in automotive vehicles, the pump is driven by the engine of the automotive vehicle with highly varying rotational speeds. In this method, the pump is dimensioned in such a way that even with no-load speeds of the engine, the necessary pressure fluid quantity is delivered. With quick movmement of the automotive vehicle and the consequent considerably higher rotational speed of the engine, the delivery flow of the pump increases many times over. This highly increased delivery flow, however, can no longer be fed to the dependant unit. Therefore, it is delivered via a flow control valve of the initially named type, which -- independant of the pressure -- passes on a certain constant delivery flow to the dependant unit and leads the excess quantity back to the reservoir.
It is an essential feature of these known flow control valves that the pump must only deliver against a pressure level which is insignificantly higher than the pressure level momentarily required at the connection to the dependant unit. For instance in dependant circulation units the pressure fluid can flow through nearly without pressure when the dependant circulation unit is not actuated. In this method, the flow control valve as well responds already under a very low pressure and discharges the excess quantity to the reservoir, also without pressure. If the dependant circulation unit is actuated, the pressure fed to it will increase. The flow control valve guarantees that a constant volume flow is fed to the dependant unit furtheron and that the excess quantity is discharged to the reservoir.
But it is an essential disadvantage of the known flow control valve that only one dependant unit can be supplied with pressure fluid at a time.